The present invention relates to a fluid for viscous coupling with high durability.
In recent years, organopolysiloxane oil such as dimethylpolysiloxane, methylphenylpolysiloxane, etc. have been used as the hydraulic fluid or the operating fluid for fluid coupling (also called "viscous coupling" (VC)), and the operating conditions are becoming increasingly severe.
In a viscous coupling (VC), a plurality of inner plates movably disposed on the driving shaft and a plurality of outer plates fixed on the driven shaft with predetermined spacings are combined together alternately and are accommodated in a housing, and dimethylpolysiloxane oil, which is a viscous fluid for torque transmission, is filled in it. Under such arrangement, shearing force, i.e. shear torque, is generated in said plate groups by the difference of the revolutions between the driving shaft and the driven shaft in order to transmit torque to the driven shaft.
As the fluid coupling (viscous coupling) of this type, dimethylpolysiloxane (also called dimethyl-silicone oil) with high viscosity index (VI) is used, but it is difficult to maintain stable torque transmission ability for a long time under severe operating conditions at high temperature. This is mainly due to the low thermal stability of dimethyl-silicone oil at high temperature. Because the operating conditions are becoming increasingly severe in various applications including the application of viscous coupling, it is an imminent problem to improve thermal stability of silicone oil, which constitutes the main component of dimethyl-silicone.
To prevent oxidation or gelation, antioxidants such as iron octanoate, phenylamine derivatives, ferrocene derivatives, etc. have been added to organopolysiloxane oil.
Although a certain level of the gelation preventive effect can be obtained at high temperature when these antioxidants are added, the viscosity increases when viscous coupling is continuously used.
The object of this invention is to offer a fluid for viscous coupling, which provides excellent effect for the prevention of thermal decomposition and gelation and is furnished with high stability.